SICP sicp 111: 3.24 exercises 1113.24 and

SICP sicp 111: 3.24 exercises 1113.24 and
Exercise 3-24 original

Exercise 3.24. In the table implementations above, the keys are tested for equality using equal? (Called by assoc ). this is not always the appropriate test. for instance, we might have a table with numeric keys in which we don't need an exact match to the number we're re looking up, but only a number within some tolerance of it. design a table constructor make-table that takes as an argument a same-key? Procedure that will be used to test "integrity" of keys. Make-table shocould return a dispatch procedure that can be used to access appropriate lookup and insert! Procedures for a local table.

Code

(define (make-table same-key?)    (let ((local-table (list '*table*)))       (define (lookup key-1 key-2)          (let ((subtable (assoc key-1 (cdr local-table))))             (if subtable                 (let ((record (assoc key-2 (cdr subtable)))                    (if record                        (cdr record)                        false))                false)))      (define (insert! key-1 key-2 value)          (let ((subtable (assoc key-1 (cdr local-table))))             (if subtable                 (let ((record (assoc key-2 (cdr subtable))))                      (if record                          (set-cdr! record value)                          (set-cdr! subtable                                    (cons (key-2 value)                                          (cdr subtable)))))                    (set-cdr! local-table                              (cons (list key-1                                          (cons key-2 value))                                    (cdr local-table)))))            'ok)        (define (assoc key records)            (cond ((null? records)                    false)                  ((same-key? key (caar records))                      (car records))                  (else                    (assoc key (cdr records)))))              (define (dispatch m)            (cond ((eq? m 'lookup-proc) lookup)                  ((eq? m 'insert-proc!) insert!)                  (else                     (error "Unknown operation -- TABLE" m))))        dispatch))

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